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Publication Three-Dimensional Resonant Exciton in Monolayer Tungsten Diselenide Actuated by Spin-Orbit Coupling(American Chemical Society, 2019-12-24) CHI SIN TANG; YIN XINMAO; Yang, Ming; Wu, Di; Birowosuto, Muhammad Danang; Wu, Jing; LI CHANGJIAN; Hettiarachchi, Chathuranga; Chin, Xin Yu; Chang, Yung-Huang; Ouyang, Fangping; Dang, Cuong; Pennycook,Stephen John; FENG YUAN PING; Wang, Shijie; Chi, Dongzhi; Breese, Mark B H; Zhang, Wenjing; Andrivo Rusydi; WEE THYE SHEN,ANDREW; PHYSICS; MATERIALS SCIENCE AND ENGINEERING; SINGAPORE SYNCHROTRON LIGHT SOURCEThe intricate features of many-body interactions and spin-orbit coupling play a significant role in numerous physical phenomena. Particularly in two-dimensional transition metal dichalcogenides (2D-TMDs), excitonic dynamics are a key phenomenon that promises opportunities for diverse range of device applications. Here, we report the direct observation of a visible-range three-dimensional resonant exciton and its associated charged exciton in monolayer tungsten diselenide, as compared to monolayer molybdenum disulfide. A comprehensive experimental study that includes high-resolution TEM, Raman, high-resolution spectroscopic ellipsometry over a wide temperature range down to 4 K, high-energy temperature, and excitation power-dependent photoluminescence spectroscopy has been conducted. It is supported by first-principles calculations to unravel the influence of spin-orbit coupling in the formation of the resonant exciton and to identify its in-plane and out-of-plane features. Furthermore, we study the impact of temperature and thickness on the spin-orbit coupling strength in 2D-TMDs. This work is crucial in creating a platform in the fundamental understanding of high-energy resonant exciton in layered two-dimensional systems and that such high-energy optoelectronic features make them an increasingly attractive candidate for novel electronic and optoelectronic applications particularly in the aspects of solar cells and light-emitting diodes via the manipulation of excitonic states.Publication Genetic variants in sporadic parkinson's disease: East vs west(Elsevier Ltd, 2012) Peeraully T.; Tan E.K.; DUKE-NUS MEDICAL SCHOOLA number of gene variants or single nucleotide polymorphisms (SNPs) have been shown to modulate the risk of Parkinson's disease (PD). These variants are identified from genetic association studies of familial PD and candidate genes, and from genome wide association studies (GWAS). These include REP1 dinucleotide repeat polymorphism within the promoter region of the SNCA gene, and SNPs within the vicinity of SNCA and LRRK2 genes. A number of exonic variants of LRRK2 (G2385R, R1628P, S1647T, M1646T, A419V, R1398H, N551K, Y2189C) have been shown to influence PD risk in various ethnic populations. Numerous GWAS linked loci including BST1 (bone marrow stromal cell antigen 1), PARK16 (parkinson disease 16 susceptibility), GAK (cyclin G associated kinase), and HLA (human leukocyte antigen) have also been identified. The genetic variants have differential effect on PD risk in Eastern and Western populations. Knowing the basis behind ethnicspecific variances would further our understanding of the pathophysiologic mechanisms and help planning of genetic testing programmes. � 2011 Elsevier Ltd.Publication LRRK2 interacts with ATM and regulates Mdm2-p53 cell proliferation axis in response to genotoxic stress(Oxford University Press, 2017) Chen Z.; Cao Z.; Zhang W.; Gu M.; Zhou Z.D.; Li B.; Li J.; Tan E.K.; Zeng L.; YONG LOO LIN SCHOOL OF MEDICINE; DUKE-NUS MEDICAL SCHOOLPathogenic leucine-rich repeat kinase 2 (LRRK2) mutations are recognized as the most common cause of familial Parkinson's disease in certain populations. Recently, LRRK2 mutations were shown to be associated with a higher risk of hormonerelated cancers. However, how LRRK2 itself contributes to cancer risk remains unknown. DNA damage causes cancer, and DNA damage responses are among the most important pathways in cancer biology. To understand the role of LRRK2 in DNA damage response pathway, we induced DNA damage by applying genotoxic stress to the cells with Adriamycin. We found that DNA damage enhances LRRK2 phosphorylation at Serine 910, Serine 935 and Serine 1292. We further showed that LRRK2 phosphorylation is abolished in the absence of ATM, suggesting that LRRK2 phosphorylation requires ATM. It should also be noted that LRRK2 interacts with ATM. In contrast, overexpression or knockdown of LRRK2 does not affect ATM phosphorylation, indicating that LRRK2 is the downstream target of ATM in response to DNA damage. Moreover, we demonstrated that LRRK2 increases the expression of p53 and p21 by increasing the Mdm2 phosphorylation in response to DNA damage. Lossof- function in LRRK2 has the opposite effect to that of LRRK2. In addition, FACS analysis revealed that LRRK2 enhances cell cycle progression into S phase in response to DNA damage, a finding that was confirmed by 5-bromo-20-deoxyuridine immunostaining. Taken together, our findings demonstrate that LRRK2 plays an important role in the ATM-Mdm2-p53 pathway that regulates cell proliferation in response to DNA damage. � The Author 2017. Published by Oxford University Press. All rights reserved.Publication Tunable black phosphorus heterojunction transistors for multifunctional optoelectronics(Royal Society of Chemistry, 2018-08-07) WANG LIN; HUANG LI; TAN WEE CHONG; FENG XUEWEI; Chen, Li; ANG KAH WEE; ELECTRICAL AND COMPUTER ENGINEERINGMany, black phosphorus (BP) based field-effect transistors, homojunctions, and vertical van der Waals structures have been developed for optoelectronic applications, with few studies being conducted on exploring the potential of their naturally formed heterojunctions. Here, we report a novel thickness-modulated, gate-tunable BP heterojunction phototransistor for multiple purposes and high performance optoelectronics. Despite its thickness of less than 5 nm, the device, whose fabrication spares the need for split-gate or chemical doping or vertical stacking requirements, achieves an excellent photoresponsivity of 383 A W-1 at 1550 nm under zero gate bias, which is among the best photoresponse performance of all-BP-based photodetectors in this spectral range. Furthermore, it exhibits a shot-noise-limited noise equivalent power (NEPshot) of less than 10-2 pW Hz-1/2, making it very promising for ultra-low power detection. Additionally, owing to the heterojunction-induced built-in electric field, the device can be readily used for infrared photovoltaic devices in the absence of source-drain bias (Vd), a feature that is distinctively superior to traditional phototransistors. The multifunctionality demonstrated in our BP heterojunction transistor paves the way towards realizing tunable improved performance optoelectronics based on 2D materials platform.Publication Targeting leucine-rich repeat kinase 2 in Parkinson's disease(2013) Chan S.L.; Angeles D.C.; Tan E.-K.; DUKE-NUS MEDICAL SCHOOLIntroduction: Parkinson's disease (PD), is a common progressive neurodegenerative disorder, and missense mutations in the LRRK2 gene are the most common single genetic cause of autosomal dominant PD and polymorphic variants modulate risk in sporadic PD. Earlier research focused on LRRK2 genetics, but with the recent discoveries of LRRK2 substrates/interactors, LRRK2-specific mechanisms are being unveiled. Areas covered: As a multi-domain protein, LRRK2 possess diverse functions that range from housekeeping, signaling to clearance of proteins. Proteins that interact with LRRK2 have drawn attention to several pathophysiologic pathways that could potentially be targeted in the development of new therapies. This review will discuss the possible physiological roles of LRRK2 based on recently reported interactors as well as place LRRK2 in the disease context. Current LRRK2 inhibition studies and reports about LRRK2 biomarkers will also be discussed as they are important considerations for LRRK2 translational treatment options. Expert opinion: The discovery of LRRK2 as a pathogenic gene in PD has contributed enormously to our understanding of clinical genetics. One of the challenges is to understand the physiologic role of LRRK2 and its specific function that gets disrupted when it is mutated. In vivo LRRK2 models have provided insights but they do not full recapitulate human PD. The identification of LRRK2 interactors opens the opportunities for identification of new therapeutic targets. Ways of quantification of kinase activity in vivo and determining what constitutes physiologic inhibition will need to be further investigated before specific pharmacologic agents can be meaningfully utilized. � 2013 Informa UK, Ltd.Publication Identifying genes in parkinson disease: State of the art(Australasian Medical Publishing Co. Ltd, 2018) Chew E.G.Y.; Foo J.N.; Tan E.-K.; DUKE-NUS MEDICAL SCHOOLPublication Infrared Black Phosphorus Phototransistor with Tunable Responsivity and Low Noise Equivalent Power(American Chemical Society, 2017-10-18) HUANG LI; TAN WEE CHONG; WANG LIN; DONG BOWEI; LEE CHENGKUO; ANG KAH WEE; ELECTRICAL AND COMPUTER ENGINEERINGThe narrow band gap property of black phosphorus (BP) that bridges the energy gap between graphene and transition metal dichalcogenides holds great promise for enabling broadband optical detection from ultraviolet to infrared wavelengths. Despite its rich potential as an intriguing building block for optoelectronic applications, however, very little progress has been made in realizing BP-based infrared photodetectors. Here, we demonstrate a high sensitivity BP phototransistor that operates at a short-wavelength infrared (SWIR) of 2 μm under room temperature. Excellent tunability of responsivity and photoconductive gain are acquired by utilizing the electrostatic gating effect, which controls the dominant photocurrent generation mechanism via adjusting the band alignment in the phototransistor. Under a nanowatt-level illumination, a peak responsivity of 8.5 A/W and a low noise equivalent power (NEP) of less than 1 pW/Hz1/2 are achieved at a small operating source-drain bias of -1 V. Our phototransistor demonstrates a simple and effective approach to continuously tune the detection capability of BP photodetectors, paving the way to exploit BP to numerous low-light-level detection applications such as biomolecular sensing, meteorological data collection, and thermal imaging.Publication Genetics: Utility of next-generation sequencing in ataxias(2013) Tan E.-K.; DUKE-NUS MEDICAL SCHOOLPublication Composition and structure of tropical intertidal hard coral communities on natural and man-made habitats(Springer, 2021-03-06) Lee YL; Lam QYS; Tay TS; Kikuzawa YP; Tan KS; TROPICAL MARINE SCIENCE INSTITUTEPublication Integration of 2D Black Phosphorus Phototransistor and Silicon Photonics Waveguide System Towards Mid-Infrared On-Chip Sensing Applications(Institute of Electrical and Electronics Engineers Inc., 2018-10-25) HUANG LI; DONG BOWEI; Guo, Xin; CHANG YUHUA; CHEN CHI-NAN; HUANG XIN; Wang, Hong; LEE CHENGKUO; ANG KAH WEE; ELECTRICAL AND COMPUTER ENGINEERINGWe demonstrate the first black phosphorus phototransistor integrated with Si photonics waveguide system towards mid-infrared (MIR) sensing. At a wavelength of 3.78 μm, the black phosphorus phototransistor achieves a high responsivity of 0.7 A/W under a small drain bias of-1 V at room-temperature. Additionally, the device offers gate and drain bias tunability to suppress dark current while simultaneously optimize photo-response performance. Our results reveal the potential of black phosphorus for MIR detection to enable the realization of integrated on-chip systems for MIR sensing applications.